1. Field of the Invention
The present invention relates to an ignition system for an internal combustion engine, which uses as a power source a magnetogenerator in association with the internal combustion engine and uses discharge voltage from a capacitor as an ignition timing signal.
2. Description of the Prior Art
An ignition system for an internal combustion engine, which uses as a power source a magnetogenerator in association with the internal combustion engine, repeats charge and discharge to and from a capacitor at every constant cycle period, and takes discharge voltage from the capacitor as an ignition timing signal, is well-known. It is important for such ignition system to eliminate a malfunction caused by signal noises and to fix the ignition timing from the start to the high speed area of the internal combustion engine.
In order to prevent the malfunction caused by noises from a signal circuit, an apparatus for by-passing needless signals (in Japanese Patent Laid-Open Gazette No. 60-6072 (1985)) and that to suppress fluctuation in the ignition timing caused by the number of revolution of the internal combustion engine (in Japanese Patent Publication No. 56-19469 (1981) have been proposed.
FIG. 1 is a circuit diagram of the ingnition system disclosed in the Japanese Patent Laid-Open Gazette No. 60-6072 (1985), in which a reference numeral 1 designates an ignition power coil mounted on a magnetogenerator and for generating AC power. A capacitor 3 charged by the ignition power coil 1 is connected thereto through a diode 2 and in series with an ignition coil 5 comprising the primary coil 6 subjected to be charged from the capacitor 3 and the secondary coil 7 outputting the secondary voltage, and an ignition plug 8 given output voltage from the secondary coil 7 to carry out spark discharge.
A reference numeral 16 in the same drawing, designates a signal coil mounted on the magnetogenerator to generate AC power, the signal coil 16 connecting to the gate of a silicon-controlled reclifier (to be hereinafter called the thyristor) and the collector of a transistor 52 through a series circuit of a diode 17 and resistance 51, the anode of thyristor 4 connecting with a node of the diode 2 and capacitor 3.
The ignition power coil 1 connects with the base of the transistor 52 through a parallel circuit of a power circuit 9 and a diode 55, the transistor 52 being subjected to base voltage from the power circuit 9 and applied between the emitter and the base with the negative wave of the ignition power coil 1 through the diode 55.
Furthermore, a series circuit of a diode 53 and resistance 54 for controlling the negative wave of the ignition power coil 1 is connected to a node of the ignition power coil 1, power circuit 9 and diode 55.
Next, explanation will be given on operation of the ignition system.
The positive wave output of the ignition power coil 1 charges the capacitor 3 through the diode 2 and is supplied to a constant voltage power circuit 9, which is given power to output constant voltage. The signal coil 16 is connected to the gate of thyristor 4 so as to be given the positive wave from the signal coil 16 through a diode 17 and resistance 51, but while the ignition power coil 1 is charging the capacitor 3 with the positive wave, the output of the constant voltage power circuit 9 keeps the transistor 52 on, so that the positive wave of the signal coil 16 is by-passed through the transistor 52.
When voltage of the ignition power coil 1 transfers to the negative wave form, a voltage drop of the resistance 54 of a current flowing through the diode 53 and resistance 54 is applied between the emitter and the base of the transistor 52 to turn the transistor off, the output of the signal coil 16 is applied to the gate of thyristor 4, which is on to deliver the charge of capacitor 3 to the primary coil 6 at the ignition coil 5, and the output voltage from the secondary coil 7 ignites an internal combustion engine.
While the capacitor 3 is being charged, the gate of thyristor 4 is by-passed and masked against noises so that, when the charging is completed to make the ignition power coil to have negative waveform, the noise mask is released and simultaneously ignition is performed. Hence, this ignition system is effective in the system which once ignites the engine per one output cycle of the ignition power coil 1.
The ignition system disclosed in the Japanese Patent Publication Gazette No. 56-19469 (1981) applies reverse bias voltage to an output of a signal coil to suppress spark advance caused by an increase in the output of signal coil during the high speed running, thereby obtaining an about constant ignition time period from the low speed running to the high speed running. Hence, this ignition system is effective in suppressing the spark advance during the high speed running.
An internal combustion engine for an outboard motor, as above-mentioned, is desired to be constant in the ignition timing from the start to the high speed stage. However, generated voltage from the signal coil mounted on the magnetogenerator has an angular width in waveform and a crest value grows as the number of revolution increases, whereby it is inevitable to cause some delay at the start area.
On the contrary, the method of applying the reverse bias voltage to the signal voltage as the ignition system disclosed in the Japanese Patent Publication Gazette No. 56-19469 (1981), is about constant in the ignition timing, but during the low speed running where the number of revolution varies, this ignition system is not stable in the ignition timing. In other words, since the capacitor is charged by the output of signal coil at the present cycle period and the charge voltage becomes reverse bias to an output of the signal coil at the next cycle period, when the number of revolution suddenly changes, the reverse bias voltage fluctuates. As a result, an excessive advance or lag in the ignition timing will occur.
The noise mask method as disclosed in the Japanese Patent Laid-Open Gazette No. 60-6072 (1985) ignites the engine simultaneously with the mask release by the negative waveform, whereby it is difficult to make constant the ignition timing, because the armature reaction of the ignition power coil causes a shift in waveform.